Polycyclic Aromatic Hydrocarbons: Sources,
Environmental Behaviour and Methods of
Analysis
Dr. A. Ramesh Kumar
Senior Scientist
Solid and Hazardous Waste Management Division
(Stockholm Convention Regional Center)
CSIR-National Environmental Engineering Research Institute
Nehru Marg, Nagpur. 440020
Scope
1. What are polycyclic aromatic hydrocarbons?
2. Sources, physico-chemical properties and environmental
behaviour
4. Analysis by HPLC
5. Questions
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What are polycyclic aromatic hydrocarbons?
• Aromatic compounds with 2 or more fused/condensed ring
• Thousands of PAHs are identified
• Plannar molecules
Naphthalene
• Dense π electrons is responsible for the persistence of
PAHs
• Low water solubility, low vapor pressure, and high melting
and boiling points
• PAHs high molecular weight decrease water solubility and
increase lipophilicity, making them more recalcitrant
Anthracene
Fluorene
• Based on occurrence, recalcitrant nature, and toxicity, US
EPA classified 16 PAHs as priority pollutants
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Phenanthrene
What is the concern ?
• Ubiquitously present in the environment
• Present at higher concentrations than other organic contaminants
• Continuous emission from various sources
• Known carcinogens (Group I and Group IIA & IIB) mutagenic, and
teratogenic potencies
• Associated with various adverse health effects
• Non-dietary ingestion is an important pathway for human exposure
• PAHs are formed during some methods of cooking
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PAHs formation during Cooking of
Food
• PAHs formed by the incomplete burning of organic
matter at temperatures over 200 C
• Method of cooking
• Grilling
• Barbeque, smoking
• Roasting
• Tandoor
PAH formation is influenced by:
1. Temperature of cooking
2. Duration of cooking
3. Type of fuel used in heating
4. Distance from heat source
5. Fat content of the food
EU limit for BaP
Oils and fats 2
μg/kg, foods for
infants/ children
1 μg/kg; smoked
meat and smoked
fish 5 μg/kg;
unsmoked fish 2
μg/kg
FSSAI limit of BaP
5 µg/kg
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How do we get exposed to PAHs?
• Breathing air containing PAHs in the workplace of coking, coal-tar, and
asphalt production plants; smokehouses; and municipal trash incineration
facilities.
• Breathing air from cigarette smoke, wood smoke, vehicle exhausts,
asphalt roads, or agricultural burn smoke.
• Coming in contact with air, water, or soil near hazardous waste sites.
• Eating grilled or charred meats; contaminated cereals, flour, bread,
vegetables, fruits, meats; and processed or pickled foods.
• Drinking contaminated water or milk.
• Nursing infants of mothers living near hazardous waste sites may be
exposed to PAHs through their mother's milk.
Polycyclic Aromatic Hydrocarbons: Sources
• Incomplete pyrolytic/combustion process
• Processing of coal, crude oil, burning of fossil fuels
• Thermal power plants, cement industries, steel a production etc.
• Biomass/wood burning
• Vehicular exhaust
• Waste incineration
• High temperature cooking
• Natural sources- forest fires, volcanic eruptions, petroleum products
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Petrogenic PAHs
• A typical crude oil may contain from 0.2 to more than 7% total PAH
• Most of the PAHs in petroleum are low molecular weight hydrocarbons
containing two or three fused aromatic rings e.g. naphthalene, anthracene,
phenanthrene
• Higher molecular weight PAHs, usually are at low concentrations (<100 ppm)
• Petrol contains mainly low molecular weight aliphatic, olefinic, and monocyclic
aromatic hydrocarbons (e.g., benzene and toluene) and 2-ring PAHs
(naphthalene and alkylnaphthalenes).
• Diesel fuels, home heating oils, and engine oils may contain aromatic
hydrocarbons from benzene through fluoranthene (four aromatic rings)
• Many of the PAHs in petrogenic PAH assemblages contain one or more methyl,
ethyl, butyl, or occasionally higher alkyl substituents on one or more of the
aromatic carbons
• Homologues with two to four alkyl carbons usually are more abundant
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Pyrogenic PAHs
• Complete combustion of organic matter ultimately produce carbon dioxide and water
• If combustion is incomplete or the combusted fuel products cool quickly, the small organic chemicals
may condense to form new chemicals, including PAH.
• PAH formed during combustion are called pyrogenic PAH
• Abundant in the vapor and particulate phases of engine exhaust.
• Two- and 3-ring PAH are most abundant in the vapor phase; 4- through 6-ringed PAHs often are more
abundant in the particulate phase (soot) of engine exhaust or smoke
• Pyrogenic PAH assemblages are complex, and are dominated by 4-, 5-, and 6-ring PAHs.
• Ratios of phenanthrene to anthracene (PH/AN) and fluoranthene to pyrene (FL/PY) are useful for
differentiating between sediment PAH assemblages containing primarily pyrogenic or petrogenic PAHs.
• Anthracene and fluoranthene are thermodynamically less stable than their isomers, phenanthrene and
pyrene, respectively
• Anthracene and fluoranthene are produced during rapid, high-temperature pyrosynthesis, but are less
favored to persist during the slow organic digenesis leading to the generation of fossil fuels.
• Thus, the PH/AN ratio of pyrogenic PAH assemblages usually is less than 5 and the petrogenic ratio
usually is greater than 5. The FL/PY ratio usually approaches or exceeds a value of 1 in pyrogenic
assemblages and usually is substantially less than a value of 1 in petrogenic PAH assemblages.10
PAHs Structural Features
PAHs are also classified on the basis of their ring structure
(a) Alternant : All rings are 6- membered benzoid ring
e.g. Anthracene, Phenanthrene and Chrysene
(b) Non-Alternant PAH
6- membered benzoid rings and 3/4/5 membered rings
e.g. Fluorene, Fluoranthene
Lower membered rings are generally formed
due lower temperature and less efficient combustion.
(c) Most PAHs consist of a “bay-region”, a “K-region”
and “L -region”.
(d) PAH are not reactive and require metabolic
activation to form electrophiles to elicit their harmful
effects, thus they are procarcinogens
(e) These bay- and K-region epoxides are chemically
reactive.
Anthracene
Fluorene
Chrysene
Fluoranthene
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PAHs formation Mechanism
• Majority of PAHs are formed during
pyrolysis/combustion under oxygen
deficient conditions
• Complex organic molecules are cracked
down to smaller unstable radicals, which
create oxygen deficient zone
• These unstable radicals, partly undergo
combustion, partly combine to form stable
molecules
• Several PAHs combine to form soot
particles
• Soot particles are major air pollutant and
linked to adverse effects on pulmonary
functions
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US EPA Priority List
of PAHs
• Selected based on their relative toxicity,
abundance, chance of exposure, and
levels in the environmental samples
• Nine out of the 16 PAHs are mostly
present in the particle phase
• TEF represents the toxicity of an individual
PAH compound
•
relative to the reference chemical—
benzo(a)pyrene.
• The total potential carcinogenic potency of
PAH mixtures is determined by
•
TEQ = Σ(PAHi x TEFi)
•
TEQ = toxic equivalents of reference
compound
•
PAH,- = concentration of PAH congener i
•
TEF; = toxic equivalency factor for PAH
congener i
Polycyclic Aromatic Hydrocarbons
Physical Properties of PAHs
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Total Toxic Equivalents of PAHs
• A single number used to denote the toxic potential
• Benzo[a]pyrene (BaP) is the highest toxic PAH-Reference PAH
• BaP, TEF value: 1
TEQ = Σ(PAHi x TEFi)
• TEQ = toxic equivalents of reference compound /BaP equivalent
• PAH- = concentration of PAH congener i
• TEF = toxic equivalency factor for PAH congener i
• Canadian soil quality standards TEQ 0.6 mg/kg for residential, agriculture,
commercial and industrial soils
• Indian soil PAH range: 0.044- 274 mg/kg (Itanagar-Bhavnagar)
• ΣBaPeq 0.0026-0.8827 mg/kg
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US EPA List of 16 PAH Priority Pollutants
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US EPA+EU combined list of 24 PAHs
• The European
Union (EU)
regulates PAHs
found primarily
in food matrices
(EU 15 +1 list)
• Eight PAHs are
common to both
lists (EU and
EPA)
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EU List of 16 PAHs
• The European Union (EU) regulates PAHs found primarily in food
matrices (EU 15 +1 list)
• Eight analytes are common to both lists (EU and EPA)
• Three critical pairs of the 15+1 EU PAHs co-elute and are difficult to
resolve by mass spectrometry
These challenging pairs are
• benz[a]anthracene-cyclopenta[c,d]pyrene- chrysene,
• benzo[b]fluoranthene-benzo[k]fluoranthene-benzo[j]fluoranthene, and
indeno[1,2,3-cd] pyrene-dibenz[a,h]anthracene.
• Agilent J&W DB-EUPAH 20 m x 0.18 mm, 0.14 μm (mid polar, 50%
phenyl/50% dimethyl) or VF-17 MS give resolution of these pairs
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EPA Methods for PAHs Analysis
• EPA 625: Base, neutrals and acids by GC-MS
• EPA 610: PAHs by HPLC & GC in water/waste water
• EPA 8270 Semivolatiles by GC-MS
• EPA 8100 PAH by GC-MS
• EPA 8310 PAH by HPLC in water/soil/soild waste
• DB-5 MS is generally used for EPA 16 PAHs
• For EU-PAHs, DB-EUPAH or VF-17 MS is useful
• Using a VF-17 MS (50% phenyl/50% dimethylpolysiloxane, mediumpolarity), GC column, a good separation of benzo[b]fluoranthene,
benzo[j]fluoranthene, benzo[k]fluoranthene can be achieved
compared to DB-5
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Source Identification of PAHs
• Fossil fuels (petrogenic PAH),
• Burning of organic matter (pyrogenic PAH), and transformation
of natural organic precursors in the environment
• by relatively rapid chemical/biological (diagenic) processes
• (biogenic PAH)
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EPA 8310 PAH by HPLC in Water/Soil/Soild waste
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Extraction
Water samples: liquid-liquid extraction with dichloromethane (EPA 3510)
Soil/sediment: Soxlet/Microwave/Ultrasonic/Accelerated solvent extraction
Clean up: column chromatography/SPE catridges
Column clean up
Silica gel: 100-200 mesh size, activate at 130 °C for 16 hrs
Sodium sulphate: activate at 400 °C for 4 hrs
Exchange extraction solvent to cyclohexane
Column packing: glass wool-Na2SO4 -silica gel-DCM slurry packing 10 g-Na2SO4
Column washing 40 ml pentane
Load sample extract, add25 ml pentane, discard pentane eluate
Elute with(2:3) DCM:pentane, collect, solvent exchange to acetonitrile (for HPLC) or
hexane (for GC)
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HPLC Method Development
• Instrument: UHPLC, Thermo Ultimate 3000, Quartnary pump,
PDA detector, Chromeleon software
• Ascentis® Express C18, HPLC Column, 2 µm particle size, L x I.D.
15 cm x 2.1 mm, reverse phase
• 90 Å, C18 (RP-18, ODS, Octadecyl), end capped, carbon load
7.2 %
• Retention mechanism: hydrophobic interaction
• Mobile phase: Water: Acetonitrile ; Gradient elution
• Elution order: increasing molecular mass, run time: 18.5 min
• Column temp: 35 °C
• Detector wavelength: Photodiode Array (PDA), 225, 229, 235,
254 nm
• wavelength chosen for calibration: 229 nm
Gradient Program
% A,
Water
% B, ACN
Time
(min)
60
40
0.5
50
0
1
40
60
1.8
30
70
3
20
80
15
60
40
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23
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Chromatograms of PAHs
Resolution of 16 PAHs
Overlay of Chromatograms
of standards
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Calibration Graphs
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Source Identification of PAHs
•
PAH isomer pair ratios were used as diagnostic indicators to
identify possible sources. Isomers have similar partitioning
behavior and solubility.
•
Anthracene / Anthracene + Phenanthrene
•
Benz[a]anthracene / Benz[a]anthracene + Chrysene
•
Fluoranthene / Fluoranthene + Pyrene
•
Indeno[1,2,3-c,d]pyrene / Indeno[1,2,3-c,d]pyrene +
Benzo[g,h,i]perylene
Table 1. PAH isomer pair ratios of specific sources
Source
PAH Isomer Pair Ratio
An/178 BaA/228 Fl/Fl+Py IP/IP+BghiP
Petroleum (unburned)
<0.10 <0.20 <0.40
<0.20
Petroleum combustion
0.40-0.50 0.20-0.50
Petroleum and combustion (mixed)
0.20-0.35
Combustion
>0.10 >0.35
Biomass and coal combustion
>0.50
>0.50
Thanks for your attention !
Questions ?
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